Plasma Cortisol and Chloride Stress Responses in Juvenile Walleyes during Capture, Transport, and Stocking Procedures

Abstract

Abstract Extensively reared juvenile walleyes Stizostedion vitreum subjected to capture and transport stressors associated with stocking procedures in South Dakota and Minnesota displayed acute increases in plasma cortisol and extended declines in concentrations of plasma chloride. In four separate South Dakota transport hauls, mean plasma cortisol in walleyes rose from 12–49 ng/mL at the time of trap-net capture to 138–174 ng/mL after 1 h of transport; these concentrations remained increased at 3 h. Plasma chloride decreased by about 19% during this period; by 3 h, mean values had dropped about 30%, to 53–61 meq/L. Similarly, in Minnesota mean plasma cortisol in captured and transported walleyes increased from 13–26 ng/mL during trap-net capture to 154–214 ng/mL by 1 h after transport in three separate trials and remained at the higher values at 3 h posttransport. Mean plasma chloride concentrations dropped about 28%, to 65–72 meq/L, by 3 h after transport and remained significantly decreased at 68–82 meq/L 24 h later, even though plasma cortisol, an acute stress indicator, had returned to near pretransport values. Results from these experimental transport hauls indicate that the juvenile walleyes experienced considerable physiological stress when captured and transported to lakes for stocking. This stress was reflected by an appreciable decrease in plasma chloride that failed to recover to pretransport values after 24 h, which suggests a possible mechanism for poststocking mortality.